When a tire rotates with load applied thereon, the tread portion generates heat and reaches a high temperature, which leads to various types of failure such as heat separation of the tread portion. In order to lower the temperature of the tread portion, it is necessary to reduce heat generation or improve heat dissipation.
Conventionally, in order to lower the temperature of the tread portion, one method has been to form grooves in the tread portion, thereby removing tread rubber that is the source of heat generation and increasing the surface area of the tread portion, which increases heat dissipation (for example, see JP 2003-205706 A (PTL 1)).
Another technique for increasing the heat dissipation effect at the tread portion is to provide a small groove extending in a direction that intersects the extending direction of a narrow groove that extends in the tire width direction, so as to disrupt the flow of air that flows in the narrow groove (for example, see JP 2007-230399 A (PTL 2)).